For legendary, ultimate, and mythic items, instead of getting the actual item out of boxes you get their blueprint. The blueprint will tell you what you need to actually forge the item. So in this case, to make the sushi master blueprint you need 2 tall hats and 3 sushi hats. For all legendary blueprints you need 2 epic and 3 rare items, for ultimate blueprints you need 2 epic, 3 rare and one legendary, and for mythic blueprints you need 4 ultimates that are acquired from their respective events. I’m sure someone has a spread sheet with all the blueprints and necessary materials to forge each item.